Many regions throughout the world, in particular regions that are subject to seismic activity, have fire, structural, seismic and other codes that must be met during the design, construction and even retrofit of a building. Such buildings may take the form of, but are not limited to, commercial buildings, office buildings, churches, schools, convention halls, theatres, and even many types of residential and multi-family complexes.
The International Building Code (IBC) is one type of code and is also the model building code that has been adopted throughout most of the United States. The IBC differs from the related International Fire Code (IFC) in that the IBC addresses fire prevention in regard to construction and design, whereas the IFC addresses fire prevention in regard to the operation of a completed and occupied building. For example, the building code sets criteria for the number, size and location of exits and types of walls in the design of a building while the fire code requires the exits of a completed and occupied building to be unblocked. The building code also deals with structural stability and seismic requirements. The IBC applies to all structures in areas where it is adopted, except generally for one and two family dwellings, which are typically covered by the International Residential Code.
By way of example, a portion of the IBC dealing with fire walls states they must meet both fire and structural requirements. More specifically, fire walls are required to be continuous from foundation to a termination point at least thirty inches above the adjacent roofs, with a number of exceptions allowing the termination at the underside of roof and fire walls must have sufficient structural stability under fire conditions to allow the collapse of construction on either side of the wall without affecting the rating of the wall. In addition, a seismic portion of the code requires that all parts of the structure between separation joints be interconnected to form a continuous load path and the interconnection forces must be below an acceptable threshold, which may be defined in the code.
The effect of structural provision is that the fire wall may not be vertically supported by either side of the wall, and must be laterally supported by both sides—where the lateral supports are required to adequately brace the wall while not being strong enough to damage the wall during collapse. The effect of the seismic provision is that unless there is a separation joint at the fire wall, then the building must be interconnected across the fire wall, while still allowing collapse on either side. However, if a separation joint is provided at the fire wall, then a significant amount of seismic drift would need to be accommodated. It is unlikely that any sort of wall brace would be consistent with an accommodation of seismic motion.
Even where the IBC has not been adopted, local building codes often require that a fire wall be located between certain rooms or adjacent an exterior space. A fire portion of the local code requires the fire wall to have a two-hour fire resistance rating. As implied in the IBC, this fire rating may be achieved by constructing the fire wall so that it is continuous from foundation to roof. The structural portion of the local code may further require the fire wall to have sufficient structural stability and strength to allow for the collapse of an opposing wall in the room, similar to the IBC. And, a seismic portion of the local code may require that all portions of the building be interconnected or otherwise structurally tied together to form a continuous load path. In short, the three primary code requirements may be summarized as a fire wall that (1) has a two-hour fire rating; (2) is sufficiently stable and strong in the event of a collapse; and (3) is interconnected with other portions of the building to form part of the continuous load path. However, meeting these three requirements generates to a multitude of design challenges, a complex installation process, and increase costs.
In stud-framed buildings, the two-hour fire rating requirement may be achieved with gypsum board (e.g., drywall, wallboard, plasterboard, etc.) assembled into a two-hour fire wall having an unbroken plane where the fire wall is independently and laterally supported on both sides. However, gypsum board is a relatively soft material with limited structural capacity, therefore concurrently achieving the structural and seismic requirements is essentially impossible unless the loads on the drywall are sufficiently low. In short, the known construction options for meeting all portions of the code relating to fire walls are limited.
FIGS. 1-4 show various fire wall systems that either currently exist or could potentially be constructed to better local code requirements. However, each option has drawbacks, whether it is the complexity of the assembly, its ability to carry load, or its ability to achieve the unbroken plane where the fire wall system is independently and laterally supported on both sides.
FIG. 1 shows a prior-art fire wall system 100 anchored by wall studs 102 and a sole plate assembly 104. Two layers of fire-rated wallboard 106, 108 are attached at least to the studs 102 on a non-floor bearing side of the system 100. Two additional layers of fire-rated wallboard 110, 112 are attached at least to the studs 102 on the floor-bearing side of the system 100. A floor girder 114, provided to carry a floor assembly 116, is structurally independent from the sole plate assembly 104 and wallboard layers 110, 112. The floor assembly 116 is secured to the floor girder 114. In the illustrated embodiment the floor assembly 116 includes a floor sheathing panel 118, floor joists 120, joist hangers 122, and fire-rated sub-floor panels 124. The fire wall system 100 does not meet all the code requirements because the system does not include interconnection anchors across the wall, in which the anchors are strong enough to resist interconnection loads, but would not damage the wall under a partial collapse condition. Even if such anchors were provided, the system 100 would be expensive and difficult to install.
FIG. 2 shows an example of alternate fire wall systems 200 mounted back-to-back to achieve seismic separation. For purpose of brevity, only one of the systems 200 will be described. The fire wall system 200 includes wall studs 202 and a sole plate assembly 204 that engages a floor sheathing panel 206 of a floor assembly 208. Two layers of fire-rated wallboard 210, 212 are attached at least to the studs 202. Two additional, non-continuous layers of fire-rated wallboard 214, 216 are attached at least to the studs 202, above and below the floor assembly 208, respectively. In the illustrated embodiment the floor assembly 208 includes the floor sheathing member 206, floor joists 218, and at least one fire-rated sub-floor panel 220. Unlike the system 100 shown in FIG. 1, the present system 200 does not include a floor girder or joist hangers. Nevertheless, the system 200 would be expensive and difficult to install.
FIG. 3 shows yet another type of fire wall system 300, which is similar to an area separation wall system described in the Gypsum Association Fire Resistance Design Manual, 17th Ed. (April 2003). The fire wall system 300 includes two fire-rated panels 302, 304 with vertical edges set into steel H studs 306 and with horizontal edges sent into upper and lower runners 308, 310, respectively. The fire wall system 300 is distinct from the adjacent stud walls while being laterally supported by either or both of the stud walls. While there are firewall-to-stud wall connectors that are designed for partial building collapse, such connectors are incompatible with seismic interconnection forces and do not have an appropriate amount of flexibility to allow both sides of the fire wall system 300 to move independently, while at the same time rigidly anchoring the fire wall system 300 to both stud walls. Thus, one drawback of the fire wall system 300 is that it is not seismically independent. In addition, the system 300 would be expensive and difficult to install.